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Nano Banana Pro Sketch: Precise AI Image Editing With Masks

How Nano Banana Pro’s Sketch tool enables pixel-safe local edits, multi-region changes, and ‘add objects’ workflows—plus practical prompt templates you can reuse.

Nano Banana Pro Sketch: Precise AI Image Editing With Masks

Nano Banana Pro quietly shipped a feature called Sketch—and it’s a big deal if you’ve ever used AI image editing and felt frustrated by collateral damage.

Instead of rewriting the whole frame, Sketch lets you mark exactly what you want to change. Anything outside the marked area stays untouched (down to the pixel). That single design choice turns AI retouching from “rolling the dice” into something you can actually control.

Note: This post is an original, practical write-up inspired by a public article discussing Sketch. I’m not affiliated with Nano Banana Pro.

What Sketch does (in one sentence)

Sketch = masked editing: you paint/outline the region, then tell the model what should change inside that region—everything else remains stable.

Image slots (paste yours here)

If you have your own screenshots or licensed images, drop them into these slots:

Why designers care: the “don’t touch anything else” promise

Classic AI editing workflows often suffer from one painful side effect: you ask for a small change, and the model “helpfully” changes unrelated details (textures, lighting, extra objects, even geometry).

Sketch flips the default:

  • You decide where the model is allowed to edit.
  • You decide what should happen in that region.
  • You explicitly instruct the model to preserve everything else.

This is exactly what you want for production design work: localized, reversible, iteration-friendly edits.

Three workflows you can steal today

1) Targeted retouching (change one thing, keep the rest)

Use it when you want a precise change like:

  • Make one apple red (leave the other fruit unchanged)
  • Replace a logo on a single sign
  • Remove a small blemish or reflection

Prompt template (single edit)

Only edit the masked/painted area.
Change: {describe the new result}
Preserve: lighting, perspective, shadows, textures, and all unmasked regions.
Do not alter the background or any other objects.
If any markup/paint/outline is visible, remove it in the final image.

Example

Only edit the masked area.
Change the green apple into a red apple with natural highlights and matching shadows.
Preserve all other fruits, the plate, background, lighting, and camera perspective.
Remove any drawn circles/paint marks from the final output.

2) Multi-region edits (one pass, multiple changes)

Some Sketch-style tools support multiple marked regions (often color-coded). That unlocks fast “variant building”:

  • Region A → swap object type
  • Region B → change color/material
  • Region C → remove object

Prompt template (multi region)

Only edit the marked regions.
Region 1 (red): {change}
Region 2 (yellow): {change}
Region 3 (green): {change}
Preserve everything outside the marked regions exactly.
Remove all circles/labels/paint marks in the final image.

Tip: keep each region instruction short and concrete. If you need styling, put it once at the end (“photorealistic product photo, soft studio lighting”).

3) “Add something” (controlled inpainting)

Sketch isn’t just for changing—it's also for creating inside the masked area:

  • Add a badge/sticker
  • Add a prop (cup, book, lamp)
  • Add a UI element in a screenshot mock

Prompt template (add object)

Only edit the masked area.
Add: {object}.
Match: perspective, scale, lighting direction, shadow softness, and material realism.
Do not modify any unmasked pixels.
Remove any sketch marks.

Example

Only edit the masked area.
Add a small enamel pin on the jacket lapel.
Match the fabric folds, lighting from top-left, and a subtle shadow on the cloth.
Do not modify any unmasked pixels.
Remove any sketch marks.

Practical prompting rules (that actually reduce re-rolls)

  • Always anchor scope: “Only edit the masked area.” Put it first.
  • Say what to preserve: “Keep lighting/perspective/shadows unchanged.”
  • Ask to remove markings: if you used circles/paint, explicitly request cleanup.
  • Describe realism constraints: scale, perspective, material, shadow softness.
  • Iterate like a designer: change one variable per attempt (color, shape, texture).

Troubleshooting checklist

  • The model changes the background → repeat “Do not modify any unmasked pixels” and keep the mask tight.
  • The mask outline stays visible → add “Remove all circles/paint marks in the final output.”
  • The inserted object looks pasted → specify light direction, shadow contact, and matching grain/noise.
  • Colors drift → mention “keep global color grade unchanged” and name the target color (e.g., “deep crimson”).

Closing thought

Sketch-style masked editing is the kind of “small UI feature” that changes the whole workflow. It makes AI editing feel less like gambling and more like a controllable tool in a designer’s pipeline.

If you want, tell me what kind of images you edit most (product photos, UI mockups, portraits), and I’ll tailor 5–10 prompt templates specifically for your use case.